In connection with the completion of oil and gas wells, it is frequently necessary to utilize packers in both open and cased boreholes. The walls of the well or casing are plugged or packed from time to time for a number of reasons. As shown in FIG. 1, for example, sections of a well 10 may be packed off with packers 16 on a tubing string 12 in the well. The packers 16 isolate sections of the well 10 so pressure can be applied to a particular section of the well 10, such as when fracturing a hydrocarbon bearing formation, through a sliding sleeve 14 while protecting the remainder of the well 10 from the applied pressure.
FIGS. 2A-2B depict portions of a downhole tool 16 in partial cross-section having a packer element 50 according to the prior art. The packer element 50 is disposed adjacent the housing 20 of the tool 16 between end rings 22, 24 and includes an inner elastomeric member 52 separated by spacers 56 from outer elastomeric members 54.
The packer element 50 may be suited for High Pressure/High Temperature applications. As such, the packer element 50 typically includes metal fold back rings 58 to contain the elastomeric elements 52, 54 from extruding and leaking due to pressures causing high extrusion forces on the elements 52, 54. The metal fold back rings 58 require a thick cross-section to contain and prevent elastomer extrusion. As shown in FIG. 2B, the thick cross-section can create scenarios where the elastomer can extrude over the top of the metal fold back rings 58 during setting of the packer element 50. This over-extrusion can lead to failure of the packer element 50.
In addition to over-extrusion, the conventional HP/HT metal fold back rings 58 typically do not completely square-off or fully pack-off during initial setting. Therefore, the metal fold back rings 58 may tend to move and square-off additional amounts after setting when the element 50 is later subjected to pressure differentials. This is typically acceptable with boosted packers, but non-boosted packers tend to leak when these additional movements occur especially during thermal cycling.
In one possible solution to the problem, the tips of the metal fold back rings 58 can be machined very thin to allow for easier expansion during setting. Although this modification can help with the rings' expansion during setting, the machining steps can be costly and can make the rings very fragile and easy to damage during handling. In another less desirable solution, the maximum temperature rating for the packer element 50 can simply be reduced, but this limits possible uses and implementations.
Therefore, a need exists for a packer for use in high pressure and high temperature applications having fold back rings capable of square-off or full pack-off during setting.
The subject matter of the present disclosure is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.